One of the most hazardous jobs firefighters and other emergency personnel must do is to enter a burning building. In this situation, the building floor plan may be unknown (and may change), visibility is impaired, and the locations of equipment and personnel may change. Combining this situation with a limited air supply and potentially obstructed escape paths results in an extremely dangerous environment.
In such an environment, there are strict limits on the amount of time a firefighter may be inside a burning building due to limitations imposed by the limited air supply and on increasing fire and smoke intensity. Additional challenges result as a consequence of the complete or partial failing of the building, which may result in the destruction of escape paths.
Pseudo-satellites, or pseudolites, are commonly known in the art as devices which transmit a GPS, or GPS-type signal, but which are located in relatively close proximity to the ground. When using pseudolites to provide navigation in an indoor, underground or obstructed environment, there is a concern that nearby pseudolites will negatively impact the ability of a receiver to track all of the available pseudolites. This problem, known as the “near-far” problem, is a consequence of limited dynamic range. Some techniques for solving this problem, such as modifying the pseudolite duty cycle or synchronizing the pseudolite transmissions have been previously proposed.
A system for locating emergency personnel in a building has been discussed in “A System of Tracking and Locating Emergency Personnel Inside Buildings” presented by Progri et al. at the Institute of Navigation (ION GPS 2000, Sep. 19–22, 2000, pp. 560–568). Similarly, techniques for dealing with the “near-far” problem have been discussed in “Techniques for Reducing the Near-Far Problem in Indoor Geolocation Systems” presented by Hill et al., at the Institute of Navigation (ION NTM 2001, Jan. 22–24, 2001, pp. 860–865). The above referenced publications and presentations are hereby incorporated herein, in their entirety, by reference.